JPS63251435A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To obtain the title film excellent in lubricity, chipping resistance and scratch resistance, etc., by adding spherical silica particles of specified properties and metal terephthalate particles of specified properties as lubricants to a polyester, forming this mixture into a film and biaxially stretching this film. CONSTITUTION:0.005-3wt.% spherical silica particles of an average particle diameter of 0.05-4mum and a particle diameter ratio (major diameter/minor diameter) of 1-1.2 and 0.005-3wt.% particles of a metal terephthalate or a metal salt containing an alkylene terephthalate component (e.g., calcium terephthalate) of an average particle diameter of 0.05-5mum are added as lubricants to a polyester (e.g., polyethylene terephthalate). This polyester is formed into a film, which is biaxially stretched to obtain the title biaxially oriented polyester film. This film is small in a void size, uniform in the irregularities on the film surface, so that is can be suitably used as a video film, etc.

Description

[Detailed description of the invention] [Industrial use! l! 'F] The present invention relates to a biaxially oriented polyester film, more specifically, a lubricant consisting of specific spherical silica particles and particles of a metal salt containing a metal terephthalate component or an alkylene terephthalate component (and a phosphorus component) is added, and the film is resistant to Scrapability,
This invention relates to a biaxially oriented polyester film that has excellent slip properties and improved scratch resistance.

[Prior Art] Polyester films, represented by polyethylene terephthalate films, have excellent physical properties.

Because of its chemical properties, it is used in a wide range of applications, such as magnetic tape, capacitors, photography, and packaging.

It is used for OHP etc.

In polyester films, their slipperiness and abrasion resistance are major factors that determine workability in the film manufacturing process and processing in each application, as well as product quality.

If any of these is insufficient, for example, when applying a magnetic layer to the surface of a polyester film and using it as a magnetic tape,
During application of the magnetic layer, the friction between the coating roll and the film surface is intense, and the film surface is also abraded, and in extreme cases, wrinkles, scratches, etc. may occur on the film surface. Furthermore, even after the film coated with the magnetic layer is slit and processed into audio, video, or computer tapes, many kite parts, playback heads, etc. Significant abrasion occurs between the layers, causing scratches and distortion, and furthermore, the surface of the polyester film is scraped, resulting in the precipitation of white powdery substances, resulting in loss of magnetic recording signals,
That is, it is often a major cause of drop-out.

Generally, to improve the slipperiness of a film, a method is adopted in which the contact area between the film and the Kiteroll is reduced by adding unevenness to the film surface, which can be roughly divided into (1)
A method of precipitating inactive fine particles from the polymeric catalyst residue used as a film raw material, and a method of (n) adding inert R-free fine particles are used. Generally speaking, the larger the size of the fine particles in these raw polymers, the greater the effect of improving slipperiness. Since this itself can be a cause of defects in dropout accommodation, it is necessary that the irregularities on the film surface be as fine as possible, and the current situation is that there is a demand to satisfy these contradictory characteristics at the same time.

In addition, in a film made of polyester containing the above-mentioned inert fine particles, peeling occurs at the boundary between the fine particles and the polyester due to biaxial stretching, and voids are formed around the fine particles. The larger this void is, the finer the particle, the more
The shape becomes more spherical than plate-like, the harder the fine particles are to deform as a single particle, the larger the stretching area M@ ratio when stretching an unstretched film, and the lower the temperature. As these voids get larger, the shape of the protrusions becomes gentler, increasing the coefficient of friction, and small scratches on the voids of the biaxially oriented polyester film that occur during repeated use can also cause particles to fall off. This reduces durability and causes the generation of shavings. Calcium carbonate and titanium oxide as inert particles.

Adding one or more types of kaolin (a combination of large particles and small particles) has been commonly practiced in the past (JP-A-51-34272, JP-A-52-78953).

JP-A-52-78954, JP-A-53-41355, JP-A-53-71154, etc.), these fine particles form large voids and therefore have the above-mentioned problem, and improvement of this problem is also desired. It is rare. Incidentally, the precipitated particles (for example, polyester oligomer metal salt, etc.) precipitated during polyester V production have small voids and have disadvantages such as poor machinability, poor running properties, and poor scratch resistance. .

[Purpose of the Invention] The present inventor has solved these disadvantages, improved the slipperiness and abrasion resistance of the film by making the voids around the inert fine particles small, and making the film surface moderately rough. The present invention was developed as a result of intensive studies to obtain a biaxially oriented polyester film with a surface suitable for various uses.

Therefore, an object of the present invention is to provide a biaxially oriented polyester film with small voids, uniform film surface roughness, even surface irregularities, and excellent slipperiness, abrasion resistance, and scratch resistance. be.

[Configuration and Effects of the Invention] According to the present invention, an object of the present invention is to
As a lubricant, 0.005 to 3% by weight of spherical silica particles (A) with an average particle diameter of 0.05 to 4 μm and a particle size ratio (major axis/minor axis) of 1.0 to 1.2 and an average of 0.005 to 3% by weight. Particle size is 0.
Particles (B) of metal salt containing terephthalic acid metal salt or alkylene terephthalate component having a diameter of 05 to 5 μm are
．． This is achieved by using a biaxially oriented polyester film containing 0.005 to 3% by weight.

Here, the major axis and minor axis of the spherical silica particles are determined from an image magnified, for example, 10,000 to 30,000 times with a scanning electron microscope after depositing a thin gold lQ layer on the particle surface.
The average particle size 1 particle size ratio is determined by the following formula.

Average particle diameter - Sum of area circle equivalent diameters of measured particles / Number of particle diameter ratio of measured particles - Average major diameter of silica particles / Average minor diameter of the particles The polyester in the present invention is a compound whose main acid component is aromatic dicarboxylic acid. It is a polyester whose main glycol component is aliphatic glycol. Such polynisdels are substantially linear and have film forming properties, particularly by melt molding. Examples of aromatic dicarboxylic acids include terephthalic acid and naphthalene dicarboxylic acid.

Isophthalic acid, diphenoxyethanedicarboxylic acid.

Diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid.

Examples include diphenylketone dicarboxylic acid and anthracene dicarboxylic acid. Examples of aliphatic glycols include polymethylene glycols having 2 to 10 carbon atoms, such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, etc. 1-
Examples include alicyclic diols such as diol and cyclohexane dimetatool.

In the present invention, polyesters containing alkylene terephthalate and/or alkylene naphthalate as a main component are preferably used.

Among such polynisdels, for example, not only polyethylene terephthalate 1- and polyethylene-2,6-naphthalate, but also terephthalic acid and/or 2,6-naphthalene dicarboxylic acid account for 80 mol% or more of the total dicarboxylic acid component, A copolymer in which 80 mol% or more of the total glycol component is ethylene glycol is preferred. In this case, up to 20 mol% of the total acid component can be aromatic dicarboxylic acids other than terephthalic acid and/or 2,6-naphthalene dicarboxylic acid, and also aliphatic dicarboxylic acids such as adipic acid, cepatic acid, etc. Dicarboxylic acid; can be an alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid. In addition, 20% of the total glycol ingredients
Up to mol% can be of the above glycols other than ethylene glycol, or for example hydroquinone,
Resorcin, 2,2-his(4-hydroxyphenyl)
Aromatic diols such as propane; aliphatic diols containing aromatic rings such as 1,4-dihydroxymethylbenzene:
polyethylene glycol, polypropylene glycol,
It can also be a polyalkylene glycol (polyoxyalkylene glycol) such as polytetramethylene glycol.

In addition, the polyester in the present invention includes, for example, human odor.
-j Aromatic oxyacid such as cybenzoic acid: A component derived from an oxycarboxylic acid such as an aliphatic oxyacid such as ω-hydroxycap-17ic acid is added at 20 mol per total dicarboxylic acid component and oxycarboxylic acid component. % or less of copolymerization or bonding is also included.

Furthermore, the polyester in the present invention contains a trifunctional or higher functional polycarboxylic acid or a polyhydroxy compound, such as trimellitic acid, in an amount in a substantially linear range, for example, an amount of 2 mol% or less based on the total acid component. , pentaerin litol, etc. are also included.

The above-mentioned polyesters are known per se and can be produced by methods known per se.

The above polyester has an intrinsic viscosity of about 0.4 measured as a solution in 0-chlorophenol at 35°C.
~0.9 is preferred.

The biaxially oriented polyester film of the present invention has many fine protrusions on its surface.

According to the present invention, these many fine protrusions are caused by two types of lubricants dispersed and contained in the polyester, namely, spherical silica particles (A) and metal terephthalate or a metal salt containing an alkylene terephthalate component. It originates from particles consisting of particles (B).

A polyester containing such a lubricant dispersedly can be prepared at any time during the reaction to form a polyester, for example, during the transesterification reaction or polycondensation reaction when using the transesterification method, or at any time when using the direct polymerization method. Alternatively, the particles described above (preferably as a slurry in glycol) may be added to the reaction system.

Preferably, the initial stage of the polycondensation reaction has an intrinsic viscosity of about 0.
It is preferable to add spherical silica particles or the like to the reaction system up to step 3. Particles (A) and particles (B) can be added individually or together.6 In the present invention, the spherical silica particles (A, ) dispersed in polyester have an average particle size of 0.05 to 4 μm. The spherical silica particles have a particle size ratio (major axis/breadth axis) of 1.0 to 1.2. These spherical silica particles have an individual shape or a spherical shape that is extremely close to a true sphere, and are either silica particles conventionally known as lubricants, ultrafine spherical particles of about 10 mm, or aggregates of about 0.5 μm. It is characterized by a marked difference from the formation of aggregates (agglomerated particles).

The average particle size of the spherical silica particles is preferably 0.1 to 3μ
m, more preferably 0.1 to 2 μm.

If the average particle diameter is less than 0.05 μm, the effect of improving slipperiness and scratch resistance is insufficient, and this is not a problem. Moreover, if the average particle diameter exceeds 4 μm, the surface of the film becomes too rough, which is not preferable. Further, the particle size ratio of the spherical silica particles is preferably 1.0 to 1.15. More preferably 1.0 to 1.
It is 1.

In addition, it is preferable that the spherical silica particles have a sharp particle size distribution, and the relative standard deviation representing the steepness of the distribution is 0.5.
Below, it is more preferably 0.4 or less, particularly preferably 0.3 or less.

This relative standard deviation is expressed by the following formula.

Relative standard deviation - where D11 area equivalent diameter of individual particles (μm) D=
Average diameter equivalent to sum of surface areas (-(Σ Di)/n) (μm) i=1 n: represents the number of particles measured.

When spherical silica particles with a relative standard deviation of 0.5 or less are used, the height of the protrusions on the film surface becomes extremely uniform because the particles are spherical and have an extremely steep particle size distribution. Furthermore, the individual protrusions on the film surface have very sharp protrusions because the voids around the lubricant are small, and therefore, even with the same number of protrusions, the slipperiness is extremely good.

As long as the spherical silica particles satisfy the conditions described above, there are no limitations on the manufacturing method or other aspects.

For example, spherical silica particles are made of ethyl orthosilicate [S
i (OC2H5) a ] to produce hydrous silica [S i (OH) 4 ] monodisperse spheres, and then the hydrous silica monodisperse spheres are dehydrated to form silica bonds [=
It can be produced by three-dimensionally growing Si -0-3i =] (Journal of the Chemical Society of Japan' 81.1109, p.
, 1503).

S j (OC2H5) a + 4) Iz O→ S
i (OH) a + 4C2H50
H3 S 4 - OH+HO-8i =→ =S
i-0-3t 壬 + ト ■ 2 0 In the present invention, particles of metal salt containing terephthalic acid metal salt or alkylene terephthalate component (hereinafter sometimes referred to as metal salt particles) (B ) has an average particle size of 0.05 to 5 μm, preferably 0.1 to 3 μm, and more preferably 0.3 to 2 μm. This average particle is 0
．． If the thickness is less than 0.05 μm, the effect of improving slipperiness and cracking resistance is insufficient, which is not preferable. Also, this average particle size is −
If it exceeds 1.4-5 μm, the surface of the film will be too rough, making it unsuitable for wives and children.

Specific examples of such metal salt particles (B) include (n-0 to
3) (Ω-0,1,2, ln=0.1) (n = O~・3) (Top=0.1,2, m20,1) (m=o,1) -15- −～ etc. can be exemplified. The metals that form metal salt particles include:
Preferred examples include alkali metals and alkali metals.

The metal salt particles (B) are not limited by the manufacturing method. As a typical example, a manufacturing example of calcium terephthalate particles will be described. A terephthalic acid aqueous solution is added to a calcium chloride aqueous solution to precipitate calcium terephthalate, and the calcium terephthalate is separated, washed with water, and dried, and then anhydrous calcium terephthalate is prepared. is dispersed in glycol such as ethylene glycol to make a slurry,
Furthermore, the slurry is subjected to a conventional particle size adjustment treatment such as a pulverization treatment,
A glycol slurry in which calcium terephthalate having a predetermined average particle size is dispersed can be obtained by performing a classification process or the like. Furthermore, particles of the ethylene terephthalate component or a metal salt containing the same and the phosphorus component can be produced by a known method for producing internally precipitated particles, but this particle production is different from the system for producing polyester in the present invention. Is it necessary to do this in another system?

In the present invention, the amount of spherical silica particles (A) added must be 0.005 to 3.0% by weight, preferably 0.01 to 1.0% by weight, based on the polyester.

More preferably, it is 0.05 to 0.5% by weight. If the amount added is less than 0.005% by weight, the effect of improving slipperiness and cracking resistance will be insufficient, while if it exceeds 3.0% by weight, the film will frequently break during the manufacturing process, which is not preferable.

Further, the amount of metal salt particles (B) added needs to be 0.005 to 3.0% by weight, preferably 0.01 to 1.0% by weight, more preferably 0.05% by weight based on the polyester.
~, 0.5% by weight. If the amount added is less than 0.005% by weight, the effect of improving slipperiness, abrasion resistance, and scratch resistance will be insufficient, while if it exceeds 3.0% by weight, the film will break frequently, which is not preferable.

The biaxially oriented polyester film of the present invention can be produced according to conventional methods for producing biaxially oriented films.

For example, a polyester containing spherical silica particles (A) and a polyester containing metal salt particles (B) are melt-mixed and extruded, melt-formed to form an amorphous unstretched film, and then the - Manufactured by biaxially stretching an unstretched film, heat setting and, if necessary, relaxing heat treatment. At this time, the film surface characteristics vary depending on the particle diameters, i, etc. of the spherical silica particles (A) and metal salt particles (B), and also depending on the stretching conditions, so they are appropriately selected from conventional stretching conditions. Furthermore, since the density, thermal shrinkage rate, etc. change depending on the temperature magnification, speed, etc. during stretching and heat treatment, conditions are determined to satisfy these characteristics at the same time. For example, the stretching temperature is either the first stage stretching temperature (for example, longitudinal stretching temperature: T1) or (T g -10)
From the range of ~ ('I''g + 45) ° C (where Tg: glass transition temperature of polyester), the second stretching temperature (for example, lateral stretching temperature 2 T2) or (Tz + 5) ~ (T1 + 4
0) It is recommended to select from the range of ℃. Further, the stretching ratio is preferably selected from a range in which the uniaxial stretching ratio is 2.5 times or more, particularly 3 times or more, and the area ratio is 8 times or more, especially 10 times or more. Furthermore, the heat setting temperature is 180 to 250
℃, preferably from the range of 200 to 230'C.

The biaxially oriented polyester film of the present invention has extremely small voids compared to conventional films, and the reason for the small voids is the affinity of the polyester of the spherical silica particles (A) and metal salt particles (B). Good sex and
Furthermore, since the spherical silica particles (A) are extremely close to true spheres, stress around the lubricant propagates evenly during stretching, and stress does not concentrate on a part of the interface between the polyester and the lubricant. It is presumed that B) is easily deformed by stretching, and stress is relaxed due to this deformation.

In the present invention, by adding spherical silica particles whose particle size distribution is extremely sharp, the distribution of protrusions formed on the surface of the polyester film is extremely uniform, and a polyester film with uniform protrusion heights can be obtained. .

By further containing metal salt particles in this film, it is possible to further improve the abrasion resistance and scratch resistance while maintaining the abrasion resistance.

Second, the axially oriented polyester film of the present invention has uniform uneven surface characteristics, excellent slipperiness and abrasion resistance, and is characterized by significantly less generation of scratches, white powder, and the like. This biaxially oriented polyester film can be widely used in various applications by taking advantage of these properties. For example, when used as a base film for magnetic recording, video, audio, corn computer, etc., excellent electromagnetic conversion characteristics, slipperiness, running durability, etc. can be obtained. Furthermore, when used in capacitor applications, low I2 coefficient of friction, excellent right homogeneity, low crushing load, high transparency, etc. can be obtained. As mentioned above, this biaxially oriented polyester film is preferably used as a base film for magnetic recording media, particularly as a base film for magnetic tapes, but is not limited thereto, and can be used for electrical applications, packaging applications, vapor deposition films, etc. It can be widely applied to other fields as well. Further, the film may be subjected to surface treatment such as easy-adhesion 7ffi coach ink, corona treatment, etc. on the moon surface or both sides. Furthermore, the film may contain third components such as antistatic agents, ultraviolet absorbers, and colorants.

[Example] The present invention will be further explained below with reference to Examples.

Note that various physical property values and characteristics in the present invention were measured as follows.

(1) Particle size of spherical silica particles There are the following conditions for particle size measurement.

1) When calculating the average particle size, particle size ratio, etc. from silica powder 2) When calculating the average particle size, particle size ratio, etc. of silica particles in a film 1) When using silica powder: Electron microscope sample stage Silica powder is scattered on top so that the individual particles do not overlap as much as possible, and a gold sputtering device is used to
A gold thin film vapor-deposited layer is formed on this surface to a thickness of 200 to 300 layers, and a scanning electron microscope is used to deposit the gold thin film to a thickness of 100 to 300 mm.
Observe at 0,000 times magnification, and use Luzex 500 manufactured by E1 Regulator ■ to determine the long diameter of at least 100 particles (
Dli), short axis (DSl), and area equivalent diameter (Di).

Then, the numerical average value expressed by these following equations is -21,
--Therefore, the major axis (D I ) and the minor axis (Ds
), represents the average particle diameter (D).

n
nDI−(Σ D li ) /n, D s = (Σ
Dsi) / n1 = 1 i = 1 D = (Σ D i ) / n 1 = 1 2) In the case of silica particles in a film: A small piece of sample film was fixed on a sample stage for a scanning electron microscope, and Sputtering equipment 'ill (JFC
The surface of the film is subjected to ion etching using an ion sputtering device (Model 1100) under the following conditions.

The conditions were to place the sample in a Pelger and apply approximately 10-3 Tor.
The degree of vacuum was increased to a vacuum state of r, and the voltage was 0.251 (V
, ion etching is carried out for about 10 minutes at a current of 12.5 InA. Furthermore, gold sputtering is applied to the film surface using the same equipment, and a scanning electron microscope is used to perform gold sputtering on the surface of the film.
Observe at 30,000 times magnification -,22-- and measure the major axis (Dli) and minor axis (
Dsi) and the equivalent diameter for area (Di). The following steps are carried out in the same manner as in 1) above.

(2) Particle size, etc. of particles other than spherical silica particles 1) Average particle diameter (DP) Shimadzu CP-50 type centrifugal particle size analyzer (Centrifuaal
Particle 5ize Analyzer)
Measure using. From the integrated curve of particles of each particle size and their existing stars, calculated based on the obtained centrifugal sedimentation curve, read the particle size corresponding to 50 mass bases 1~ and calculate this value.
- The average particle size is as follows (see Bookr Particle Size Measurement Technique, published by Nikkan Kogyo Shimbun, 1975, pp. 2, 242-247)
.

2) Particle size ratio A small piece of the film is fixed and molded with epoxy resin, and an ultra-thin section (cut parallel to the film flow direction) with a thickness of approximately 600 mm is created using a microtome. The cross-sectional shape of the lubricant (particles) in the film was observed using a transmission electron microscope (model I-800 manufactured by Hitachi, Ltd.), and expressed as the ratio of the long axis to the short axis of the particle. It is expressed as the average value of the cross-sectional shape.

3) Relative standard deviation value Measurement is carried out in the same way as for spherical silica.For non-spherical particles, the volume is calculated from the particle size ratio in the film thickness direction, and the particle size is calculated using the diameter when it is an equioblate sphere. diameter, and calculate the relative standard deviation value.

(3) Film surface roughness (Ra) This is the value defined in Monthly 5-BO601 as the center line average (Ra). ). The measurement conditions are as follows.

(a) Stylus tip radius = 2μm (b) Measuring pressure: 30mm (C) Cutoff: 0.25mm (d) Measuring length: 0.5mm (e) How to summarize data Repeatedly measure the same sample 5 times , the largest value is 1
The average value of the remaining four data is rounded off to the fourth decimal place and displayed to the third decimal place.

(4) Void ratio The area around the lubricant in the film (on the surface) is exposed according to the method (11-2) above, and the long axis of at least 50 solid particles and the long axis of the voids are measured, and the long axis void ratio of the void is expressed by the following formula - 111111--------- Expressed as the number average value of the void ratio determined by the major axis of the solid fine particles.

(5) Film friction coefficient (μk) temperature 20°C1
In an environment with 60% humidity, a film cut into medium 1/2 inch pieces was attached to a fixed rod (surface roughness 0.3 μm) at an angle θ = (15
2/180 ) π radians (152°) and move (friction) at a speed of 200 am/min. The exit tension (T'z:g) when the tension controller is adjusted so that the entrance tension] ゛1 is 35g is -25~ after the film has been fed for 90m. Calculate the running wear coefficient μk.

μk = (2,303/θ) loq (Tz /
T z )=0.86810gfTz /35> (6) Scrapability The scratchability of the running surface of the base film is evaluated using a 5-stage mini super calender. The calendar is a 5-stage calendar with nylon rolls and steel rolls, the processing temperature is 80°C, and the linear pressure applied to the film is 200 kg.
/an, the film speed is 50 m/min. After running the running film for a total length of 2000 m, the abrasion resistance of the base film was evaluated based on the dirt that adhered to the top roller of the calendarer. ◎ No stains on the nylon roll ○ Almost no stains on the nylon roll (8) Scratch resistance 1/2 inch 15 on a stick
Thickness and depth of scratches on the surface of the film after running 10 m at a speed of 20 cm/sec and repeating this 50 times.

The numbers are combined and judged in the following five stages.

◎ 1/2 inch rLJ film shows no scratches 0 1/2 inch film shows almost no scratches △ 1/2 inch [[J film shows scratches ( Some thick scratches or scratches can be seen on the 1/2 inch film xx 1. / Comparative Examples 1 to 9 in which many thick and deep scratches were observed on the entire surface of a 2-inch wide film Dimethyl terephthalate and ethylene glycol were used, manganese acetate was used as a transesterification catalyst, antimony trioxide was used as a polymerization catalyst, and phosphorous acid was used as a stabilizer. was further added with additive particles shown in Table 1 as a lubricant, and polymerized in a conventional manner to obtain an intrinsic viscosity (orthochlorophenol, 35°C).
0.62 of polyethylene terephthalate was obtained.

This polyethylene terephthalate pellet was heated to 170°C.
After drying for 3 hours at
Melt at 0-300°C, and add 1 mm of this molten polymer.
Formed and extruded on a rotating cooling drum with a surface finish of about 0.35 and a surface temperature of 20°C through a slit-shaped die of 200°C.
An unstretched film of μm was obtained.

The unstretched film thus obtained was preheated at 75°C, and further heated by one IR heater with a surface temperature of 900°C from 15 mm above between low-speed and high-speed rolls to increase the temperature by 3.6 times. The film was stretched to 100° C., rapidly cooled, then fed to a stenter, and stretched 3.7 times in the transverse direction at 105° C. The obtained biaxially oriented film was heat-set at a temperature of 205°C for 5 seconds,
A heat-set biaxially oriented film with a thickness of 15 μm was obtained.

The properties of this film are shown in Table 1.6 The calcium terephthalate particles used here were prepared by the following method.

A 5 wt % aqueous sodium terephthalate solution was added to a 10 wt % aqueous calcium chloride solution to form a white precipitate of calcium terephthalate. This calcium terephthalate was separated, washed with water, and then heated at 200°C to form an anhydrous salt. This calcium terephthalate anhydrous salt was ground in a ball mill, dispersed in ethylene glycol to form a slurry, and then classified to obtain a calcium terephthalate glycol slurry having a predetermined particle size.

Examples 1 to 8 Biaxially oriented polyester films were obtained in the same manner as in Comparative Examples 1 to 2, except that two types of additive particles not shown in Table 2 were used as lubricants.

The properties of these films are shown in Table 2, and these films are excellent in abrasion resistance, runnability, and scratch resistance.

Claims (1)

[Claims] 1. In polyester, as a lubricant, the average particle size is 0.0
5 to 4 μm and a particle size ratio (major axis/breadth axis) of 1.0 to
Particles (B) of metal salt containing terephthalic acid metal salt or alkylene terephthalate component, containing 0.005 to 3% by weight of spherical silica particles (A) of 1.2 and having an average particle size of 0.05 to 5 μm. A biaxially oriented polyester film containing 0.005 to 3% by weight of. 2. The biaxially oriented polyester film according to claim 1, wherein the spherical silica particles (A) have a relative standard deviation expressed by the following formula of 0.5 or less. Relative standard deviation = ▲There are mathematical formulas, chemical formulas, tables, etc.▼ Here, Di: Area circle equivalent diameter of each particle (μm) D: Average value of the area circle equivalent diameter ▲ There are mathematical formulas, chemical formulas, tables, etc.▼ n: Represents the number of particles. 3. The biaxially oriented polyester film according to claim 1, wherein the particles (B) are calcium terephthalate.